This is an example showing how to drag and and drop UIViews between other UIViews in iOS.

Illustrates the drag and drop UIView stack

The example is broken into the following four and a half step.

Example broken into steps
1. register a UIPanGestureRecognizer to be able to get drag panning events (in our case drag events).
2. detect if the panning started above the view we would like to drag.
3. move the view according to the panning - which means removing the object from the view we would like to drag it from.
4. when dragging ends, drop the view onto the view below the dragged object.
4.a. optionally reset the dragged object, if the object is dragged onto a view which we don’t consider as a valid drop view.

In my example I have created a more or less generic DragDropManager, which is responsible for actually handling the UIViews objects we allow to drag ‘n drop and the UIVeiws we allow to drop onto.

Step 1
The manager registers the draggable objects and drop areas and takes care of detecting when a object should be dragged and dropped. This is done by receiving pan events from the UIPanGestureRecognizer. I recommend registering the gesture recognizer to a UIView having a frame covering the entire drag and drop area, because if you bind the recognizer to the actual draggable objects, you will loose the pan sequence as soon as you change super view for the dragged object (and changing super view is the hole point of dragging objects between UIViews).

Step 2
The manager switches on the different states of the UIPanGestureRecognizer and detects if a panning starts on one of our dragSubjects. If so we store the DragContext containing the dragged view and the starting point (to be able to snap back to the offset in case the drag ends outside a drop zone). At the same time we change superview for the dragged object, by attaching it to the UIView spanning the entire area. This is done to ensure our UIView is shown above all other subviews and hence is visible during the entire drag drop session.

Step 3
During the drag process we simply move the object according to the coordinates of the UIGestureRecognizer.

Step 4
When the panning ends (the UIGestureRecognizer is in state UIGestureRecognizerStateEnded), we check to see if the dropped view is above any registered drop areas. If so, we add the dragged UIView as a subview of the detected drop area.

Step 4.a.
If we don’t recognize a valid drop area beneath our dragged view, we snap the dragged UIView back to its original superview and position.

Room for improvements
- animations should be added to show more smooth look and feel.. This blog post demonstrates how to add animations to the snap back to orignial position.
- Consider the visible order of the views when selecting draggable UIView, if multiple draggable UIViews is stacked upon each other.

I have seen a couple of iPhone apps using an UITabBarController having an arrow showing just above the selected UITabBarItem as an extra visual pointer to the current visible view. At the same time the arrow moves animated between the items as the user selects them.

I decided to try implement the same effect and I have shared my solution here.

The solution is made generic enough to handle any number of UITabBarItems in the UITabBarController and basically what it does is:

In the viewDidAppear selector, the arrow is places above the first element. This is done by calculating the size and location (also known as the CGRect) of the first UITabBarItem. Then a new UIImageView is created and positioned centered and above the UITabBarItem. Again some math is used to find the offset to use for the newly created UIImageView

In the didSelectItem a transition is used to animate the movement of the arrow between the items as they are selected.

If you need to log sql statements using hibernate you can turn debug on for the org.hibernate.sql logger.
That will log all sql statement, but the actual parameter values will not be logged.

To log the values bound to the hibernate prepared statements, you can turn on trace for the org.hibernate.type logger.

Unfortunately (apparently because of perfomance) the value of the org.hibernate.type logger is evaulated once in a static block, and cached, see: EnumType.java.

That prevents you from turning the log on and off during runtime using a simple jsp page like the log4jAdmin.jsp. Note that if it were possible you still had to add trace to the page as debug is currently the lowest value.

Of course there must be a reason why the hibernate implementation are caching the value of the org.hibernate.type logger, but I believe it is still valuable to be able to turn on sql logging with parameters at runtime.

For that purpose I came across the logDriver. A simple database driver written by Ryan Bloom, that is wrapping an existing jdbc driver.

To use the logdriver all you have to do is set the driver and connection url as follows:

Yesterday I created a appengine project testing the JPA/Spring/Wicket stack.

This was created using the build.xml file found in the appengine documentation. It all worked fine, but I would like to build my project using maven so I started looking for a good maven plugin.

I found this blog talking about what features a good plugin should contain and a guy from the kindleit company claiming that they actually had implemented a maven-gae-plugin capable of executing most of these tasks.

Unfortunately I ran into several problems using this plugin, hence I have created an issue.

Untill these tasks in the issue has been fixed I would like to use another plugin.
Can anybody guide me in the direction of a more stable plugin?

Everytime I have a new machine or a new ssh access to setup I forgot how to configure the access so I don’t have to type the username each time (if I login with a different user).
At the same time I would like to use a private rsa key. So here goes a note to myself and other scatter brains